Hi Dom Tuk, I think most of UK is blurred as they haven't yet got around to taking low enough photographs of it. If the photograph is taken from a high distance then it will look okay viewed from a distance but there will be no detail when you try to zoom in.
It'll depend on the resolution of the photos. I can see the tree in blossom in my garden (the photo must have been taken in May). But when I look at another town I lived in I can see the waves in the harbour - but everything on land is extremely blurry. I have no idea why this should be, or who decides that the sea will interest people more than the town centre.
It's from satellite photography, the satellites are about 90 miles up. there's a lot better resolution photography available, but its difficult to complain about Google Earth as it's the whole world for free!